/*
 * Copyright (c) 1996, 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.util.zip;

import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;

/**
 * An input stream that also maintains a checksum of the data being read.
 * The checksum can then be used to verify the integrity of the input data.
 *
 * @author David Connelly
 * @see Checksum
 */
public class CheckedInputStream extends FilterInputStream {

  private Checksum cksum;

  /**
   * Creates an input stream using the specified Checksum.
   *
   * @param in the input stream
   * @param cksum the Checksum
   */
  public CheckedInputStream(InputStream in, Checksum cksum) {
    super(in);
    this.cksum = cksum;
  }

  /**
   * Reads a byte. Will block if no input is available.
   *
   * @return the byte read, or -1 if the end of the stream is reached.
   * @throws IOException if an I/O error has occurred
   */
  public int read() throws IOException {
    int b = in.read();
    if (b != -1) {
      cksum.update(b);
    }
    return b;
  }

  /**
   * Reads into an array of bytes. If <code>len</code> is not zero, the method
   * blocks until some input is available; otherwise, no
   * bytes are read and <code>0</code> is returned.
   *
   * @param buf the buffer into which the data is read
   * @param off the start offset in the destination array <code>b</code>
   * @param len the maximum number of bytes read
   * @return the actual number of bytes read, or -1 if the end of the stream is reached.
   * @throws NullPointerException If <code>buf</code> is <code>null</code>.
   * @throws IndexOutOfBoundsException If <code>off</code> is negative, <code>len</code> is
   * negative, or <code>len</code> is greater than <code>buf.length - off</code>
   * @throws IOException if an I/O error has occurred
   */
  public int read(byte[] buf, int off, int len) throws IOException {
    len = in.read(buf, off, len);
    if (len != -1) {
      cksum.update(buf, off, len);
    }
    return len;
  }

  /**
   * Skips specified number of bytes of input.
   *
   * @param n the number of bytes to skip
   * @return the actual number of bytes skipped
   * @throws IOException if an I/O error has occurred
   */
  public long skip(long n) throws IOException {
    byte[] buf = new byte[512];
    long total = 0;
    while (total < n) {
      long len = n - total;
      len = read(buf, 0, len < buf.length ? (int) len : buf.length);
      if (len == -1) {
        return total;
      }
      total += len;
    }
    return total;
  }

  /**
   * Returns the Checksum for this input stream.
   *
   * @return the Checksum value
   */
  public Checksum getChecksum() {
    return cksum;
  }
}
